The invention pertains to circuit board manufacturing technology, and in particular to the removal of four-sided surface mounted integrated circuits.
The manufacturing of circuit boards has moved largely from circuit boards in which the integrated circuits and other components have pass-through pins which are soldered on the opposite side of the circuit board from the body of the component, to surface-mount technology. Using surface-mount technology, integrated circuits and some other components have short leads which curl under the component, rather than projecting outwardly. The curled leads are soldered to conductor pads on the same side of the circuit board as the component.
In most circuit board manufacturing, the boards are tested at quality control points during assembly to insure that the components are working as they are designed to after the mounting process. Depending on the complexity and expense of the circuit board, if it is found to be malfunctioning it may either be discarded, or the faulty component removed and replaced. This invention relates to the removal of faulty components.
Components having pass-through pins are relatively easy to remove because the solder is on the planar, unobstructed surface opposite the side of the circuit board to which the components are mounted. Hot solder baths, on which the inventor of the instant invention has patents pending, can be applied to the pins of the suspect component to melt the solder and enable the component to be popped off from the opposite side.
However, this technique obviously cannot be used with surface mounted components. For surface mounted components, the instant applicant has developed a line of long, relatively sharp soldering blades which can be applied along an entire row of pins on an integrated circuit, either to solder them or to desolder them for removal from the circuit board. These tools can be used to remove components having two rows of leads, on opposite sides of the component. With the elongated soldering blade, the sides can be sequentially heated and lifted from the board.
However, this technique will not work with surface mount components having leads on all four edges of the chip. Obviously, if one row of leads is heated to melt the solder, but the solder is still solid on the other three sides, the heated side cannot be raised from the board.
According to current circuit board manufacturing techniques, there is no problem-free way of removing surface mount components having a four-sided lead array. The problem is complicated by the fact that one of the principle advantages of surface mount technology is that it allows the more compact mounting of components, particularly the enabling of the mounting of components on both sides of the board. To further effectuate this goal, the components are mounted together in a fairly close configuration, so that an attempt to melt the solder on one row of leads is likely to affect the integrity of adjacent solder connections on nearby components.
This is the downfall of the currently available tool which is most adequate for the job. This tool is a specialized nozzle for a hot air gun which directs hot air in four elongated streams simultaneously to the four rows of surface mount leads. The nozzle is provided in a number of different sizes and each size fits around and over a particular size IC, forcing the hot air directly at the leads on all four sides.
The problem lies in the fact that there is no way, when directing relatively large quantities of very hot air at the leads of the component to be removed, to prevent adjacent components from being affected. Thus, the suspect component can be removed and replaced, only to find that the removal process has caused electrical discontinuities in adjacent components.
There is thus a need for some tool or some technique which could adequately heat and remove the solder from the leads of a four-sided, surface mounted, integrated circuit without affecting closely spaced, adjacent components.